The present invention relates to a pneumatic, radial ply, runflat tire whose runflat handling is improved by providing a structural means for stiffening the tread and its underlying support structure. More specifically, the invention relates to a runflat tire having increased rigidity laterally across the tread to resist-upward buckling of the center part of the tread and its underlying structure during high-speed runflat operation, whereby the tread""s ground contact, lateral grip and runflat operational life is enhanced.
Various methods have been devised for enabling the safe continued operation of unpressurized or underpressurized vehicle tires with the intent of minimizing further damage to the uninflated tire and without simultaneously compromising vehicle handling over a distance from the place where the tire has lost its pressure to a place desired by the driver, such as a service station, where the tire can be changed. Loss of tire pressure can result from a variety of causes, including puncture by a foreign object such as a nail or other sharp object piercing the pneumatic tire installed on a vehicle.
Pneumatic tires designed for sustained operation under conditions of unpressurization or underpressurization are also called runflat tires, as they are capable of being driven in the uninflated or xe2x80x9cflatxe2x80x9d condition. The conventional pneumatic tire, when operated without inflation, collapses upon itself, its sidewalls buckling outward in the region where the tread contacts the ground, when supporting a vehicle load. In general, the term xe2x80x9crunflatxe2x80x9d means that the tire structure alone has sufficient rigidity and strength to support the vehicle load when the tire is operated in the uninflated condition. The sidewalls and internal surfaces of the tire do not collapse or buckle onto themselves, and the tire does not otherwise contain or use other supporting structures or devices to prevent the tire from collapsing.
An early example of a runflat tire design is described in U.S. Pat. No. 4,111,249, entitled the xe2x80x9cBanded Tire,xe2x80x9d in which a hoop or annular band approximately as wide as the tread is circumferentially deployed beneath the tread. The hoop in combination with the rest of the tire structure could support the vehicle weight in the uninflated condition.
Numerous methods have been used to achieve workable runflat tire designs. Generally, such tires incorporate sidewall designs that are thicker and/or stiffer, so that the tire""s load can be carried by an uninflated tire with minimum adverse effects upon the tire itself and upon vehicle handling until such reasonable time as the tire can be repaired or replaced. The methods used in sidewall stiffening include the incorporation of circumferentially disposed inserts in the inner peripheral surface of the sidewall portion of the carcass, which is the region in the tire usually having the lowest resistance to deformation under vertical loading. In such runflat tire designs, the sidewalls are thickened in a way that each is approximately uniformly thick in the sidewall region between the bead and the tread. The reinforced sidewalls of such tires, when operated in the uninflated condition, experience a net compressive load. The outer portions of the reinforced sidewalls are in tension due to bending stresses which deflect the sidewalls outward or apart from one another in the regions of the sidewall adjacent to the ground-contacting portion of the tread. The inner portions of such reinforced sidewalls, in the region near where the tread contacts the ground, tend to be in compression during runflat operation. Due to the large amounts of rubber required to stiffen the sidewall members, heat buildup due to flexure of the sidewalls is a major factor in tire failure, especially when the uninflated tire is operated for prolonged periods at high speeds.
A Goodyear patent U.S. Pat. No. 5,368,082 (""082) disclosed a low aspect runflat pneumatic radial ply tire which employs special sidewall inserts to improve stiffness. Approximately six additional pounds of weight per tire was required to support an 800 lb load in this uninflated tire. This earlier invention, although superior to prior attempts at runflat tire design, still imposed a weight penalty that could be offset by the elimination of a spare tire and the tire jack. This weight penalty was even more problematic when the engineers attempted to build high-aspect-ratio tires for large luxury touring sedans. These taller sidewalled tires, having aspect ratios in the 55% to 65% range or greater, means that the sidewall bending stresses are greater than that of the earlier low-aspect-ratio runflat tires disclosed in the ""082 patent. Thus the sidewalls of high profile tires had to be stiffened to the point of compromising ride characteristics, a result that is not generally acceptable for luxury vehicles, even to achieve runflat capability. The engineering requirements for runflat tire design are striving to achieve no loss in ride or handling. In the very stiff suspension performance type vehicle, such as sport cars and various sport/utility vehicles, the ability to provide such runflat tires is relatively straightforward compared to providing similar runflat tires for luxury sedans which require softer ride characteristics. Light trucks and sport utility vehicles, although not as sensitive to ride performance, provide a runflat tire market that ranges from accepting a stiffer ride to demanding the softer luxury type ride.
Considering runflat tire design in greater detail, it is typically based on the installation of one or more inserts inside each sidewall flex area. The inserts in each sidewall, in combination with the plies, add rigidity to the sidewalls in the absence of air pressure during runflat operation. While the high resistance to compressive deflection of the inserts provides the necessary resistance to the collapse of the uninflated loaded tire, this method has several drawbacks which include the above mentioned increase in tire weight and, especially during runflat operation, heat buildup in the insert reinforcements of the sidewalls.
Moreover, during runflat operation, the thick, reinforced sidewalls tend to transmit bending stresses to the portion of the tread that contacts the ground. The result is that the central portion of the tread tends to buckle upward from the ground. The upward buckle reduces the ground contact in the tread""s central region, resulting in compromised vehicle handling as well as reduced runflat tread life.
A number of prior art patent references disclose solutions to problems relating to runflat tire operation. The European Patent Application EP-A-0 605 177 (BRIDGESTONE CORP) discloses a pneumatic radial tire including at least one tie-element layer for resisting force generated in width directions of the tire. French Patent Application FR-A-2 460 218 (KLEBER COLOMBES) discloses a pneumatic radial including supports for runflat operation. French Patent Application FR-A-2 425 334 (KLEBER COLOMBES) discloses a pneumatic radial tire having runflat inserts in the sidewalls. European Patent Application EP-A-0 778 164 (BRIDGESTONE) discloses a pneumatic radial tire having runflat capability and an auxiliary layer between the carcass and the belt layer. French Patent Application FR-A-2 287 350 (GOODRICH) discloses a pneumatic radial tire having runflat capability and reinforcement members 12.
Besides the problems from tread buckling, the cyclical flexure of the tread during runflat operation tends to cause excessive heating of the tread and sidewall materials, especially during high-speed, runflat operation. The excessive heating leads to deterioration of the tire structure in the region of the tread and sidewall and thereby reduces the runflat tire""s operating life in the runflat mode. A hypothetically perfect runflat tire would be able to maintain the central portion of its tread in the same degree of road contact during runflat operation as during fully inflated operation.
It is an object of the present invention to provide a runflat radial tire as defined in one or more of the appended claims and, as such, having the capability of being constructed to accomplish one or more of the following subsidiary objects.
One object of the present invention is to provide a runflat radial tire having a laterally and circumferentially stiffened tread that resists upward buckling during runflat operation.
Another object of the present invention is to provide a runflat radial tire having a laterally and circumferentially stiffened tread that resists upward buckling during runflat operation by adding one or more compression-bearing reinforcements to the steel belt structure.
Another object of the present invention is to provide a runflat radial tire having a laterally and circumferentially stiffened tread that resists upward buckling during runflat operation by adding one or more tensile-bearing reinforcements across, and radially inward of, the crown region of the ply structure.
Another object of the present invention is to provide a runflat radial tire having a laterally and circumferentially stiffened tread that resists upward buckling during runflat operation by adding one or more compression-bearing reinforcements to the steel belt structure and one or more tensile-bearing reinforcements across, and radially inward of, the crown region of the ply structure.
Still another object of the present invention is to provide a runflat radial tire having a laterally and circumferentially stiffened tread that gives superior high-speed runflat handling characteristics by improving the tread""s runflat contact with the road by adding one or more compression-bearing reinforcements to the steel belt structure and/or one or more tensile-bearing reinforcements across the crown region of the tire in the region radially inward of the ply structure.
Yet another object of the present invention is to provide a runflat radial tire having a laterally and circumferentially stiffened tread that gives superior runflat service life as a result of reduced tread flexure which is obtained by means of adding one or more compression-bearing reinforcements to the steel belt structure and/or one or more tensile-bearing reinforcements across the crown region of the tire in the region radially inward of the ply structure.
The present invention relates to a pneumatic radial ply runflat tire having a tread, a casing with two insert-reinforced sidewalls, two inextensible annular beads, a radial ply structure, a belt structure located radially between the tread and the radial ply structure, one or more circumferentially deployed compression-stress-bearing belt reinforcing layers adjacent to or distributed within the belt structure, and/or one or more circumferentially deployed tensile-stress-bearing fabric reinforcing layers located in the region adjacent to or distributed within the radial ply structure. The cords of the one or more belt reinforcing layers are aligned between about 20 degrees to 90 degrees with respect to the equatorial plane of the tire, and are made of metal. The reinforcing cords of the one or more fabric reinforcing layers are oriented between about 20 degrees to 90 degrees with respect to the equatorial plane of the tire. The one or more metal belt reinforcing layers are deployed adjacent to the belt structure, within the belt structure or are separated from one another by the belt structure or by individual belts of the belt structure. The one or more fabric reinforcing layers are deployed adjacent to the crown portion of the radial ply structure, within the ply structure or are separated from one another by the ply structure or by individual plies of the ply structure. The one or more belt reinforcements and/or one or more fabric reinforcements contribute to the lateral rigidity of the tread and underlying structures of the carcass. At least one of the tire""s radial plies might be reinforced with inextensible metal cords.
In one embodiment of the invention, the pneumatic runflat radial tire has low-aspect-ratio (in the range of about 30% to about 50%) design. Such an embodiment has potential for runflat use in high-performance sports type vehicles or light trucks. This low-aspect-ratio radial ply runflat pneumatic tire contains two circumferentially deployed metal belts deployed radially inward of the tread surface, tread radial plies, a belt reinforcing layer and a fabric reinforcing layer. The fabric reinforcement layer has reinforcing cords that are oriented more or less laterally across the crown region of tire. The belt reinforcement layer has metal reinforcing cords also oriented more or less laterally across the crown region of tire. The metal belt reinforcement layer contributes compressive strain resistance to the belt structure, while the fabric layer contributes tensile strain resistance to the ply structure during underinflated or uninflated conditions. During runflat operation, the improved lateral and circumferential rigidity of the tread contributes to better vehicle handling and stability during high-speed, runflat operation. The improved lateral and circumferential rigidity also decreases the runflat cyclical flexure of the tread that can cause heat build which can accelerate the deterioration of the tire.
A second embodiment of this invention relates to a high-aspect-ratio (in the range of about 50% to about 80%) version of the low-aspect-ratio version for a high-profile tire. An example of a use of high-profile embodiment would be in luxury-type vehicles, high-standing sport-utility vehicles, and some light trucks. During runflat operation, the improved lateral rigidity of the tread contributes better runflat tire life and better vehicle handling and stability during high-speed runflat operation.
A third embodiment of this invention relates to a radial ply runflat tire having at least one radial ply which is reinforced by essentially inextensible cords such as steel.
A fourth embodiment of this invention relates to a radial ply, runflat tire having two compressive-stress-reinforcing reinforcement layers deployed such that one of them is located radially outward of the radially outer-most belt while the other is located between the two belts. This tire can also include two tensile-stress-bearing fabric reinforcement layers deployed such that one fabric layer is located radially inward of the radially inner-most-ply while the other fabric layer is located between the two plies.